As is known, in recent years, cellular telephones have become so widely used as to now form part of so-called mass technology, and are therefore also frequently used in vehicles by both drivers and passengers.
As is also known, various factors contribute towards making the passenger compartment of a vehicle fairly noisy. Some are related to normal operation of the vehicle, such as engine noise, and others to operation of devices which now form part of standard equipment on mass-produced vehicles, such as car radios.
All these noise sources make it difficult to hear incoming calls on a cellular telephone inside the passenger compartment of the vehicle, by partly or completely drowning out the sound of the ringer. The problem is further compounded when, as often happens, the cellular telephone is placed inside a receptacle in the passenger compartment or inside a handbag, or is set to indicate incoming calls by means of vibration (vibracall).